1. Field of the Invention
The invention generally relates to an earphone. More particularly, the invention relates to a negative pressure earphone.
2. Description of the Prior Art
In the conventional earphones, a moving-coil sound-generating unit works according to the principles of electromagnetism and Fleming's left-hand rule. As electricity is fed to the sound generating unit, a diaphragm starts to vibrate. However, as the earphone is attached to an ear, a rapid air flow is generated and causes the diaphragm to deform and generate the unpleasant noises.
Please refer to FIG. 5, which illustrates the conventional earphone. The earphone comprises a main body 1, a cover portion 2, a silicone gel earplug 3, a filtering net 4 and a moving coil sound unit 5. The silicone gel earplug 3 is fitted to the protruding end 111 of the main body 1. The filtering net 4 is provided on the opening of the protruding end and the moving coil sound unit 5 is disposed inside the main body 1. The cover portion 2 is fitted to the other end of the main body 1. One or more holes or openings 10 and 11 are provided in the main body 1 and the cover portion 2. The moving coil sound unit 5 is disposed inside the main body 1. Generally speaking, in the prior art, the moving coil sound unit 5 may have better performance of low-pitched sounds at the cost of the performance of medium-pitched and high-pitched sounds; similarly, the moving coil sound unit 5 may have better performance of high-pitched sounds at the cost of the performance of low-pitched sounds. Moreover, with the presence of these openings 10 and 11, to achieve the optimal sound performance is relatively difficult.